Most outside lines are 4". Have you located yours?In the Seattle area, the toilet can be installed with a medium 90 el or a "closet bend" that is even tighter. The 4"x3 closet bend takes up the least amount of space with the 4" on the upper flange end, the 3" on the outlet.

Have you considered raising the floor of the addition, or at least some part of the bathroom?I hate to put a step in a bathroom though, nobody expects them.

: I am planning an addition to the back of my house (in San Jose, CA) that includes a full bathroom. The foundation for the addition is concrete slab with peremeter footings. I am looking for options to get enough slope fall for the sewer line. I was hoping to connect to the sewer line at a clean out at the back of my house. There currently is a concrete patio over the pipe. As far as I can tell (without digging) the end of the pipe is 3 inch diameter and is 12 to 15 inches below grade. The bathroom is 40 to 44 feet away from the clean out. Using the 1/4" per foot slope requirement for 3" dia. pipe will require 11 inches of fall for this line. This does not include the height of the long sweep that is required for the toilet. I know 4" dia. pipe allows for a 3/16" to 1/8" per foot slope. It does not make sense to neck down to a 3" dia. pipe. Can I find a low height toilet and build a pedestal to raise it up. I would also have to raise the shower pan. I have heard of sewage power ejection systems. Is this a reasonable solution?